Activation of human Type I Fc receptors (FcgammaRI) triggers diverse cellular functions including the stimulation of the NADPH oxidase pathway. Stimulation of this pathway through FcgammaRI has been partially defined and is likely to be the result of a transient excitatory pulse initiated during the activation of FcgammaRI. The aim of this proposal is to study molecular changes in FcgammaRI during activation that could be a part of this signaling mechanism. First, FcgammaRI will be studied for hitherto unidentified subunits or proteins associated with the non-activated receptor since these proteins may be necessary for its functional integrity or may be involved in signaling. Then, activated FcgammaRI will be examined for the association of additional proteins that could be signaling mediators. Proteins associated with the non-activated and with the activated FcgammaRI will be identified and characterized. Since several different FcgammaR, and some non-Fc receptors, stimulate the oxidase pathway, presumably common mediating proteins are utilized. Therefore, the association of the characterized proteins with other oxidase-triggering receptors will be examined. In addition, the possible role of phosphorylation in the regulation of the activity or distribution of FcgammaRI will be determined. Some inhibitory conditions that block oxidase activity will also be examined. If these conditions inhibit early events in receptor activation, they may stabilize an otherwise transient activation complex and thus facilitate the study of early activation events. At the present time, the molecular basis of signaling is only poorly understood. Detailed study of FcgammaRI activation should provide valuable insights into the transient transmembrane event that triggers the oxidase response and possibly other diverse cellular functions.